Real-time detection of focal position of workpiece surface during laser processing using diffractive beam samplers

Cao, Binh Xuan; Hoang, PhuongLe; Ahn, Sanghoon; Kim, Jeng-o; Sohn, Hosik

doi:10.1016/j.optlaseng.2016.05.008

Cited by 19 publications

(6 citation statements)

References 16 publications

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“…1a). [21][22][23][24][25][26] In the marker-based approach, the fluorescence or scattering from bright particles is collected through a dedicated channel distinct from the imaging channel. 27,28 By monitoring these fiducial markers, their drift can be cor-rected.…”

Section: Introductionmentioning

confidence: 99%

Astigmatism-based focus stabilisation with universal objective lens compatibility, extended operating range and nanometre precision

Rahmani,

Cox,

Thamaravelil Abhimanue Achary

et al. 2024

Preprint

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Focus stabilisation is vital for long-term fluorescence imaging, particularly in the case of high-resolution imaging techniques. Current stabilisation solutions either rely on fiducial markers that can be perturbative, or on beam reflection monitoring that is limited to high-numerical aperture objective lenses, making multimodal and large-scale imaging challenging. We introduce a beam-based method that relies on astigmatism, which offers advantages in terms of precision and the range over which focus stabilisation is effective. This approach is shown to be compatible with a wide range of objective lenses (10x-100x), typically achieving <10 nm precision with >10 um operating range. Notably, our technique is largely unaffected by pointing stability errors, which in combination with implementation through a standalone Raspberry Pi architecture, offers a versatile focus stabilisation unit that can be added onto most existing microscope setups.

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Section: Introductionmentioning

confidence: 99%

Astigmatism-based focus stabilisation with universal objective lens compatibility, extended operating range and nanometre precision

Rahmani,

Cox,

Thamaravelil Abhimanue Achary

et al. 2024

Preprint

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“…Cao et el. recently developed methods involving a defractive beam samplers [164], as well as hole-mask, separate interrogation source [165,166] and multiple intermediate bulk-optic elements and a CCD to place the target in the focus of the machining beam. By monitoring the change in diffraction pattern on the CCD, these techniques allow for determination of the workpiece position along the optical axis and the direction of defocusing.…”

Section: Introductionmentioning

confidence: 99%

Penscriptive Depth-Controlled Robotic Laser Osteotomy

Jivraj¹

2021

Preprint

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Bone cutting in surgery is currently done using un-intelligent tools that depend on the proficiency of the surgeon to prevent damage to underlying critical structures. As one can imagine, damage isn’t always prevented. Iatrogenic damage to dura and sub-dural neural structures during osteotomical procedures such as a craniotomy can result in increased patient morbidity. This dissertation proposes the development of a robot-guided laser osteotome (bone cutter) with the use of inline optical coherence tomography (OCT) to precisely control the cutting depth in real-time. The all-fiber system design integrates a high peak-power pulsed Yb-doped fiber laser (1064nm) coupled directly into the sample arm of a swept-source OCT system (λc = 1310nm) with a fourth-order power disparity between the OCT system and fiber laser. Sub-millimeter accuracy was achieved in percussion drilling of phantom and porcine bone. Through the use of optical topographic imaging (OTI), this work presents a novel method for the surgeon to identify arbitrary trajectories for desired cuts. A surgical pencil is used to demarcate cutting trajectories for the robot to follow directly onto the boney surface. OTI imaging combined with a novel algorithm developed through this work allows the penscribed line to be isolated and translated into spatial attitude information for the robot to guide the end effector-mounted laser along. Sub-millimeter trajectory following accuracy was achieved. This work also demonstrates the first use of OCT in continuous, real-time refocusing of the optical end-effector in order to maintain cut quality. The focus of the laser was able to be maintained within the Rayleigh length of the focused Gaussian beam for linear feed rates up to 1mm/s at a 45◦ surface incline. Finally, optimization of bone ablation is explored in this dissertation. The use of graphite as a high-absorption topical chromophore and the use of nitrogen as an assist gas in the form of a coaxial jet are both analyzed to determine how to achieve the highest etch rate in bone. The results in this dissertation show that the topical application of graphite was able to significantly reduce the mean and variance of etching performance; an improvement by at least two orders of magnitude in the time to 0.5mm etch depth is demonstrated. It is also demonstrated that etch rate during ablation can be optimized for coaxial nitrogen flow (30SCFH out of a nozzle with 3mm output diameter); higher and lower flow rates showed slower etch rates. It is hypothesized that a system such as the one developed in this dissertation will increase the precision of bone cutting, decrease the amount of time needed to make cuts into sensitive structures and also address certain issues of unsuccessful uptake of lasers in modern medicine.

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“…Most DOEs are transparent surface relief microstructures that can affect either the amplitude or the phase of optical radiation passing through them [ 2 , 3 , 4 , 5 , 6 ]. They are standard in use as diffusers [ 7 ], beam splitters [ 8 ], beam samplers [ 9 ], beam shapers [ 10 ], axicons [ 11 ], vortex phase plates [ 12 ], etc. Lately, they have also found application in products such as 3D displays [ 13 ], consumer electronics [ 14 ], VR/AR/MR displays [ 15 ], automotive vehicles [ 16 ], and in fields such as robotics [ 17 ] or medically-required and elective surgery [ 18 , 19 ].…”

Section: Introductionmentioning

confidence: 99%

Electrically Tuneable Optical Diffraction Gratings Based on a Polymer Scaffold Filled with a Nematic Liquid Crystal

et al. 2021

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We present an experimental and theoretical investigation of the optical diffractive properties of electrically tuneable optical transmission gratings assembled as stacks of periodic slices from a conventional nematic liquid crystal (E7) and a standard photoresist polymer (SU-8). The external electric field causes a twist-type reorientation of the LC molecules toward a perpendicular direction with respect to initial orientation. The associated field-induced modification of the director field is determined numerically and analytically by minimization of the Landau–de Gennes free energy. The optical diffraction properties of the associated periodically modulated structure are calculated numerically on the basis of rigorous coupled-wave analysis (RCWA). A comparison of experimental and theoretical results suggests that polymer slices provoke planar surface anchoring of the LC molecules with the inhomogeneous surface anchoring energy varying in the range 5–20 μJ/m2. The investigated structures provide a versatile approach to fabricating LC-polymer-based electrically tuneable diffractive optical elements (DOEs).

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Real-time detection of focal position of workpiece surface during laser processing using diffractive beam samplers

Cited by 19 publications

References 16 publications

Astigmatism-based focus stabilisation with universal objective lens compatibility, extended operating range and nanometre precision

Astigmatism-based focus stabilisation with universal objective lens compatibility, extended operating range and nanometre precision

Penscriptive Depth-Controlled Robotic Laser Osteotomy

Electrically Tuneable Optical Diffraction Gratings Based on a Polymer Scaffold Filled with a Nematic Liquid Crystal

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